Feels like it probably should be additional optional package, because of different app and SMTP supplier requirements.
However, if you are planning to add email queuing, and brief look at both Laravel and Symphony documentation they don't seem to have it, can you please add "priority".
We are using AWS SES to send all our web app emails and user newsletter through same bespoke CI email system.
AWS has timed send limit, and their guidelines suggested on failure to try and send email again in 5 minutes. We ended up adding date field to DB, a bit like reverse expiry, emails are only considered ready for sending if time in that field has passed ( NOW() + 5 minutes ). Technically this also can help with Google Inbox "Undo send" feature.
There are 7-10K newsletters going out in rate of about 50 a minute. So we also implemented "priority" for messages, where lets say password reset request or very important app notification is priority #1, and newsletter is priority #7. Higher (or mathematically speaking, lower) priority emails are always sent before lower priority ones.
In future version we also want to implement sent email archive, probably 1 DB table for email body and description, a table for actively queued email IDs, "ready-for-send" dates, and a table for events (sent, failed /w reason/debug, ...).
Interesting that Laravel uses one shared queuing system.
